Sound absorbent and heat insulating fiber slab

ABSTRACT

A sound absorbing and heat insulating fiber slab containing cellulose fibers which are bonded together with the aid of an inorganic, flame-proof binder is characterized in that the binder belongs to the group of polymeric silicates which dry at room temperature. The binder is homogeneously distributed in the slab and bonds mutually adjacent fibers in a punctiform fashion, to form a coherent matrix. The slab has a density of from 30 to 70 kg/m 3  and the binder is present in an amount of 1-20 percent by weight.

The present invention relates to an absorbent and heat insulating fiberslab which comprise cellulose fibers bound together by means of aninorganic flame-proof binder.

By flame-binder is meant here a binder which can only be ignited withdifficulty and which is self-extinguishing.

One important advantage afforded by cellulose-fiber based slabs is thatthe fibers do not present a health hazard, as opposed to asbestosfibers, mineral wool fibers and glass wool fibers for instance, whichmust be handled with extreme caution when in a free, unbound state.Distinct from fibers of this last mentioned kind, cellulose fibers arealso suited for transportation with the aid of pneumatic devices and areable to pass through transporting fans without being hacked into smallpieces.

It is known to impregnate cellulose fibers with, for instance, asolution of water glass and to press the resultant mass into a compactsheet or web.

Such sheets, however, to a large extent lack sound absorbing and heatinsulating properties and are unable to fulfill the intended functionin, for instance, prefabricated building elements or wall structures,mainly because the originally flexible fibers are so tightly packedtogether, and so impregnated with binder as to become totally rigid.Consequently, it is a prime object of the present invention to provide afiber slab or a fiber mat of the kind defined in the introduction inwhich the individual fibers are, to a large extent, joined to oneanother by punctiform adhesive bonds, and in which said individualfibers have not been impregnated with binder and retain a high degree ofmobility in the formed slab and therewith the ability to convertacoustic energy to thermal energy, and in which the fibers enclose airinclusions therebetween, such as to be heat insulating.

This object is realized to the full with the inventive fiber slab orfibre web defined in the claims, and described hereinafter withreference to the accompanying drawings, in which

FIG. 1 illustrates plant machinery for manufacturing the inventiveslabs;

FIG. 2 illustrates in larger scale a slab forming chamber and a blowersection co-acting therewith;

FIG. 3 illustrates the capillary effect utilized in forming the stable,open structure or fiber matrix; and

FIG. 4 is a simplified illustration of the construction of the fibermatrix.

FIG. 1 is a simplified illustration of plant machinery according to theinvention. It is assumed in the following description that the inventiveslabs are formed from a cellulose-fiber starting material, fluff, thismaterial optionally being formed into continuous lengths which aresubsequently cut, e.g. sawn into slabs of desired length measurements.Referring to the plant machinery illustrated in FIG. 1, in themanufacture of a continuous cellulose fiber web, cellulose fibers(fluff) are fed into a cyclone 1, through an infeed opening 2, and arethen introduced into a mixer 3, where the fibers are mixed with air. Thefiber/air mixture is passed from the mixer 3 to a portioning or meteringunit 4, which dispenses said mixture in given quantities per unit oftime, with the aid of a feed screw not shown. The metered quantities offiber mass are drawn by suction into a conduit 6 connected to the inletside of a fan 5, and are transported in the form of a suspension througha further conduit 7 to an elongated, tapering accelerating nozzle 8,from where the mass or suspension enters a forming chamber 9. During thepassage along the tapering accelerating nozzle 8, the individual fibersin the suspension are imparted kinetic energy of such high value thatwhen exiting from the nozzle 8, the fibers will enter the formingchamber 9 in an essentially rectilinear movement path. The top andbottom surfaces of the forming chamber 9 are defined by twosubstantially mutually parallel air permeable, endless belts 10 and 11.The belts 10 and 11 extend over rollers 12, 13, 14, 15, 16 and 17, ofwhich at least the rollers 13 and 16 are driven, for instance by themotor 18 which drives the belt 10. The belts 10 and 11 are driven atmutually the same speed, in the direction of the arrows shown. Theforming chamber 9, defined at top and bottom by the two belts 10 and 11,is defined in its vertical extension by air impermeable walls, of whichthe rear wall 19 is marked in FIG. 2. The forming chamber 9 will thushave a width which corresponds to the width of the air permeable belts10 and 11 and a vertical extension, or height, which corresponds to thevertical spacing of the mutually opposing parts of belts 10 and 11. Theoutlet 21 from the forming chamber 9 (see FIG. 2) is completely open tothe exit orifice 8' of the nozzle 8, which exit orifice will preferablyhave a width which corresponds to or is slightly smaller than the widthof the forming chamber 9, whereas the outlet 21, on the other hand, canbe closed by means of a closing roller 35, which is preferably made oflightweight material, for instance foamed plastics. The roller 35 can beraised so as to expose the outlet opening 21, described herebelow. Forthe purpose of guiding the fiber suspension exiting from the nozzleorifice 8', a blow chamber 28 is provided upstream of and in connectionwith the forming chamber inlet 20. The blow chamber 28 may be configuredto form together with the blow nozzle 8 an injector, such that ambientair will be drawn into the gap between the impervious outer wallsdefining the exit orifice of the funnel-shaped nozzle and the tworollers 12 and 17, therewith engendering an overpressure in the blowcontainer. The forming chamber 9 has arranged along the entire lengththereof suction boxes 22 and 23 which generate an underpressure in theforming chamber 9. The two suction boxes 22 and 23 are connected to asuction fan 27 or some other suitable suction source, via the opening24, 25 and a conduit 26. The plant machinery illustrated in FIG. 1includes an adhesive container 29, provided with a pump (not shown), forfeeding a highly liquid, polymeric silicate binder through a pipe 30 toa spray mozzle 31, which is intended to form in the blow container anadhesive mist which settles on the fibers moving therethrough. Theformed slab or web 32 is moved out of the forming chamber 9 by the belts10 and 11, and is transferred onto a conveyor, for instance a rollerconveyor. One such roller conveyor is indicated by a roller 34.Depending on whether the slab 32 shall be subjected to heat treatment,pressing, cutting or some other working process, the slab is transportedto a drying chamber, a press means or a cutter. When the slab dischargedfrom the forming chamber already has the means or a cutter. When theslab discharged from the forming chamber already has the intendedlength, which can be achieved by intermittent feeding of fibers to themixer 3, each slab thus produced may be used immediately, provided thata quick-drying adhesive is used and provided that it is not necessary totrim the end surfaces of the slab. In the case of the illustrated,exemplifying embodiment the slabs produced are provided on the outersurface with, for instance, a layer of tissue having a surface weight,or grammage, of 18 g/m³ or therebelow, or a non-proven fabric, thismaterial being drawn in lengths from two storage reels 33 and 33' andapplied to the mutually facing surfaces of the air permeable belts 10and 11. The provision of such layers is not absolutely necessary,however, and when a quick-drying adhesive is used, e.g. a silicateadhesive, the fibers may be allowed to come into direct contact with thetwo belts 10, 11, since any adhesive which might settle on the belts 10,11 will dry and be removed from the belt surfaces during passage of thebelts over the rollers 12, 13, 14 and 15, 16, 17.

The modus operandi of the illustrated plant machinery will now bedescribed with reference to FIGS. 2 and 3. The fibers used in theillustrated embodiment are cellulose fibers and it is assumed that theslab produced will be ready for use upon manufacture and that the slabwill be flame-proof, in addition to effectively dampening sound. Inorder to be able to produce a ready-for-use slab, e.g. a slab whichrequires no heat treatment, it is necessary to use an adhesive whichwill dry rapidly at room temperature, while the desired sound dampingproperties of the slab require the cellulose fibers to be practicallyfree from impregnation and to retain their mobility. A flame-proof slabcan be obtained by using, for instance, a prepolymerized alkali silicateof the type sold commercially under the trade name Bindzil FK10. Thisbinder is diluted with up to 100 percent by weight water. A binder whichwill dry quickly at room temperature and which is completely dry whenthe slab leaves the forming chamber 9 is a requirement in achieving asound dampening ability which exceeds the sound dampening ability of aconventional glass fiber slab or mineral wool slab of the same density,meaning that the adhesive shall not be allowed to penetrate into thecavities of the cellulose fibers and render the fibers rigid subsequentto drying of the adhesive.

As described in the aforegoing, the fibers leave the outlet orifices 8'of the accelerator nozzle and the velocity of the exiting air stream andthe kinetic energy of each individual fiber is such that the fibers willmove rectilinearly, or at least substantially rectilinearly, into andout of the blow chamber 28. A mist of highly liquid and quick-dryingsilicate adhesive is generated in the blow chamber, by means of thenozzles 31, which may be directed transversely to or in the direction ofthe fiber flow. A thin layer of adhesive will be applied to at least themajor part of the fibers in the fiber flow, and the fibers will flowrapidly into the forming chamber, up to the location of the stop roller35, against which a fiber slab wall 36 is build-up. This fiber slab wall36 is moved rapidly against the fiber flow, and the belts 10 and 11 areset into motion when the fiber slab wall 36 is located, for instance, inthe position shown in FIG. 2, the speed of said belts 10 and 11 beingadjustable. As the slab formed between the fiber plate wall 36 and thestop roller is moved to the right in FIG. 2 when starting up the belts10, 11, the roller 35 will be displaced obliquely upwards/forwards tothe position shown in full lines, therewith exposing the outlet 21 ofthe forming chamber 9. The speed of the belts 10 and 11 is adjusted tocorrespond to the amount of fiber material supplied and the increaseddensity of the slab, meaning that the fiber slab wall 36 will besubstantially stationary. The adhesive-moistened fibers move in thedirection of the longitudinal axis of the forming chamber 9 and areessentially uniformly distributed by the nozzle 8 over the upstandingwall or end surface of the plate 32 extending perpendicularly to themovement direction of the fibers. The two suction boxes 23 and 24 havethe essential purpose of removing from the rearward part of the formingchamber 9, as seen in the direction of movement, air which has beeninjected into the chamber and against the wall 36, thereby to preventthe occurrence of a turbulent state, which would otherwise prevent thefibers from passing essentially at right angles to the wall or the endsurface 36 and, instead, pass onto the belts 10 and 11 or, in thepresent case, onto the air permeable tissue webs. In the case of theillustrated embodiment, a suction effect also prevails behind the endsurface 36, which contributes in withdrawing by suction a large amountof the thin-bodied silicate layer on the coated fibers. This removal bysuction of the adhesive results in impregnation of the tissue webs suchas to provide a practically fire-proof slab, when using a silicateadhesive of the aforesaid kind, while the fibers located inwardly of thesilicate-drenched tissue layers will obtain the desired sound dampingproperties and remain flame-proof or essentially flame-proof. FIG. 3 isa simplified view of two fibers 37, 38, which have been "displaced"against the end surface 36. The fiber 38 has been coated over the wholeof its surface with a layer 39 of highly liquid, thin-bodied silicateadhesive, whereas adhesive 40 has been applied to a smaller surface areaof the fiber 37. It is well known that two mutually intersecting fiberswill be bound together by capillary forces, owing to the absorption ofthe adhesive at the point of intersection, as illustrated to the rightin FIG. 3, therewith forming bonding droplets 41, 42, 43, whereas theremaining parts of the fiber will at most be coated with a very thinadhesive layer. Thus, the fibers present in the finished slab will bebonded to one another in a such as to form a matrix in which the fiberscannot be displaced and which, in turn, will mean that when the slab ismounted vertically, for instance, the density of the slab will notchange in the manner of a conventional, mineral-wool slab or aglass-wool slab, i.e. the fibers in the slab will not "avalanche" in amanner to result in a region of high density within the lower part ofthe slab and a region of lower density within the upper part of saidslab. A slab produced in the aforedescribed manner, i.e. with mutuallybonded fiber intersection points, and only a very thin coating on thefiber surfaces located externally of the intersection points, will have,in addition to flame resistance, an acoustic damping property which ishigher than the acoustic damping property of, for instance, amineral-wool slab of the same density and thickness. This improved soundabsorption is due to the fact that the cellulose fiber cavities do notabsorb the quickly-drying adhesive and thus retain their elasticity and,since the adhesive layer which at least substantially covers the fibers,does not alter to any appreciable extent the mobility of each individualfiber between its fixed intersection points, the acoustic energy will bereadily converted to kinetic energy and therewith engender oscillationsin the fibers in the three-dimensional matrix consisting of fibers whichare mutually bonded in a punctiform fashion. The density of a slabproduced in accordance with the invention may be caused to vary indifferent ways, for example by changing the amount of fiber present inthe fiber suspension and by modifying the kinetic energy of eachseparate fiber.

FIG. 4, is a simplified illustration which shows how fibers aresuccessively supplied to the formed end wall or end surface 36 of theslab. As beforementioned, the individual fibers are moved axiallytowards the end surface 36. FIG. 4 illustrates three fibers 44, 45 and46 moving towards said end surface. The leading end of the fiber 46 hasreached the end surface 36 and, because the part of the slab that hasalready formed is slightly porous, is able to penetrate some shortdistance into an open pocket in the fiber wall. It is assumed, however,that the end surface, 36 will function in the manner of a continuousabutment surface and that when the leading end of, for instance, thefiber 46 reaches the abutment surface, the fiber is stopped by the endsurface 36 and will begin to bend towards said end surface 36, asillustrated by the fiber 47, to form an arc 47' for example. Asindicated by the fibers 48, 49 and 50, there is thus formed a fibrenetwork or matrix, of which the illustrated fibers 48 and 49 have beenadhesively bonded together at their mutual intersection point 51.

The number of bonding points 51 will be contingent on the amount ofadhesive supplied, on the amount of adhesive that is removed by suction,and on density, and has been found to lie between 5 and 40 for each 100fibers present at a relatively low adhesive addition, for instance 1-20percent by weight, calculated on slab density, which was from 30 to 70kg/m³.

I claim:
 1. A sound absorbing and heat insulating fiber slab comprisingcellulose fibers bonded together by means of an inorganic, flame-proofbinder, characterized in that the binder belongs to the group ofpolymeric silicate binders which dry at room temperatures, said binderbeing homogeneously distributed in the slab and binding mutuallyadjacent fibers in a punctiform fashion to form a coherent matrix; inthat the individual fibers are not impregnated with but are only thinlycoated with binder and retain a high degree of mobility in the formedslab between their fixed intersection points; wherein the matrixexhibits from 5 to 40 bonding points calculated on each 100 fiberspresent; in that the slab has a density of 30-70 kg/m; and in that thebinder is present in an amount of 1-20% by weight.
 2. A fiber slabaccording to claim 1, characterized in that the binder is aprepolymerized alkali silicate.